Shouldn't be that hard at all by trial and error. Just get some known-weight field tips or inserts and rubber-band them to the tip of your arrow and find the balance point. Then measure to get difference of midpoint length to balance point and put numbers into FOC calculator online. Simply add or subtract weights to the end in order to dial in FOC desired. Using this method, I took arrows from a little over 400 grains total weight, with about 11 % FOC up to 680 grains, with 29 % FOC. After figuring how much tip weight was necessary, simply ordered inserts and tips to total that amount (100-gr. brass insert with 75-gr. adapter for 225-gr. Tuffhead broadhead). May want to read Ashby reports on benefits of heavy arrows with high FOC %. BTW, Colorado's parks and wildlife depts' elk university website now features an article on the benefits of heavy arrows and high FOC for penetration. Shot placement is certainly critical, but animals move and arrows may have to penetrate bone for a clean kill. No such thing as too much penetration in either case (flesh only vs. bone hit).

You have two choices. Build a heavy slower arrow with the FOC you are looking for, or stay with a lower FOC on the arrow at the weight and speed you want.

I don't hunk with that arrow length there is anything you can do to increase the tip weight without making the arrow way underspined. And to fix that you will have to go with a stiffer arrow, which will add weight, and slow you down.

I ask again why do you think 16% is such a crucial number? IMO you will smoke check everything you shoot at with your current set up, provided you hit in the right spot.

You have two choices. Build a heavy slower arrow with the FOC you are looking for, or stay with a lower FOC on the arrow at the weight and speed you want.

I don't hunk with that arrow length there is anything you can do to increase the tip weight without making the arrow way underspined. And to fix that you will have to go with a stiffer arrow, which will add weight, and slow you down.

I ask again why do you think 16% is such a crucial number? IMO you will smoke check everything you shoot at with your current set up, provided you hit in the right spot.

i understand. But you are going to have to sacrifice one or the other. If you want to hit them with a sledge hammer, you will have to lose speed. If you want fast, then you will be hitting them with a framing hammer.

If you use gold tips arrow builder you can play around with different arrow weights and lengths to get your FOC where you want it. Buy notice how heavy the total arrow weight will be, and how much slower you will be shooting.

A 400+ grain arrow shot at just about any speed will pass through any animal you shoot with it provided you don't hit big bones. You aren't going to build an arrow to knock a deer or pig off their feet when it hits them.

Will you please tell me what is so special about this 16%. Was it because someone told you that is what you need to be effective?

i understand. But you are going to have to sacrifice one or the other. If you want to hit them with a sledge hammer, you will have to lose speed. If you want fast, then you will be hitting them with a framing hammer.

If you use gold tips arrow builder you can play around with different arrow weights and lengths to get your FOC where you want it. Buy notice how heavy the total arrow weight will be, and how much slower you will be shooting.

A 400+ grain arrow shot at just about any speed will pass through any animal you shoot with it provided you don't hit big bones. You aren't going to build an arrow to knock a deer or pig off their feet when it hits them.

Will you please tell me what is so special about this 16%. Was it because someone told you that is what you need to be effective?

There's nothing particularly special about 16%.
While perusing Dr. Ashby's website tuffhead.com
I saw this and thought it'd be cool to try and build a High FOC Arrow.

There are a several categories of forward of center (FOC) used to describe the percentage of weight forward an arrow has.
Normal FOC = 0 percent to 12 percent
High FOC= 12 percent to 19 percent
Extreme FOC =19 percent to 30 percent
Ultra Extreme FOC = more than 30 percenthttp://www.tuffhead.com/education/formulas_FOC.html

Im shooting a 419 grain arrow
Its 29.5" long
My FOC is 11.4% i'd like to get it over 16. Does anyone know many more grains I need to add up front?

the general rule of thumb is 20 grains will get you 1-2% depending on a couple of variables ( like shaft gpi and length etc...). if you have enough spine its as simple a loading up the front of the arrow or you could shed an equal amount off the rear of the arrow for similar results.

Ok. What that article neglects to point out is the relation of total arrow weight to FOC and spine. And without that information it is easy to think it can be achieved without sacrificing something.

Like I have said every time, you can get a 16% FOC pretty easy but not with the current arrow you shoot, and no where near the same total arrow weight or speed.

High or above average FOC means you have to build a heavy slow arrow. Average FOC means you can buy just about any properly spined arrow and shoot standard components and normal weight broadheads and shoot higher speeds.

Play around with this to see what you come up with. Adding another 100 grains to the front would get you over 16% but it will under spine your arrows and get them way over your current weight. And that will slow you down.

If you want hard and fast, shoot a gun. Otherwise you'll have to pick one or the other.

I disagree. I have a 430 grain set up with 19% and there are several bows out there that can get 300+ fps @ launch with it. don't know how much faster and harder you want than that, it can kill anything on the continent.

I disagree. I have a 430 grain set up with 19% and there are several bows out there that can get 300+ fps @ launch with it. don't know how much faster and harder you want than that, it can kill anything on the continent.

I disagree. I have a 430 grain set up with 19% and there are several bows out there that can get 300+ fps @ launch with it. don't know how much faster and harder you want than that, it can kill anything on the continent.

Sorry but 430 grains is not "heavy", thus its "hard" hitting capabilities are limited. Can it kill most anything in North America? Sure but that doesn't necessarily constitute "hard" hitting. Lets take say a 600-650 gr arrow, now that will be a hard hitting arrow. It may not be moving as fast but it will hit like a ton of bricks. In this instance, you have momentum in your favor. It goes back to the slow sledge hammer vs fast claw hammer comparison. I put it like this, would you rather be hit by a smart car doing 60 or a freight train doing 40? Now there will be some arrows in the 425-475 range that will no doubt hit good a hard but not in relation to something a full 100-200 gr heavier.

Sorry but 430 grains is not "heavy", thus its "hard" hitting capabilities are limited. Can it kill most anything in North America? Sure but that doesn't necessarily constitute "hard" hitting. Lets take say a 600-650 gr arrow, now that will be a hard hitting arrow. It may not be moving as fast but it will hit like a ton of bricks. In this instance, you have momentum in your favor. It goes back to the slow sledge hammer vs fast claw hammer comparison. I put it like this, would you rather be hit by a smart car doing 60 or a freight train doing 40? Now there will be some arrows in the 425-475 range that will no doubt hit good a hard but not in relation to something a full 100-200 gr heavier.

Dude said "fast and hard", nothing about "heavy" reread the post. I never said 430 was heavy, I don't need a lesson in physics on arrow lethality. People are running around killing animals with arrows I built in their quivers so I fairly we'll versed On the
subject.

I've read all the replies so far and am sorry I forgot to mention a few more details about my set up.
My bow is a 65# bow that's pulling 68#s.
My arrows are approximately 29 1/8ths inch long 340 spine.
Per the Beman arrow chart I'm on the bubble if 340/300 spine.
Per the Goldtip chart I'm in the middle of the 340 spine.
I'm leaning towards the Goldtips because of less GPI.
Giving me the option of adding more weight up front and still maintain my goal of 290 fps.
290 fps at 420 grains gives me 78.2? KE. I forget the Momentum off the top of my head.
I'm willing to sacrifice speed for more FOC.
But like has been mentioned already with my current setup, with a well placed shot I know I can take anything in North America.
I'd like more FOC. But don't have the budget or equipment ,yet, to do a lot of experimenting.

Dude said "fast and hard", nothing about "heavy" reread the post. I never said 430 was heavy, I don't need a lesson in physics on arrow lethality. People are running around killing animals with arrows I built in their quivers so I fairly we'll versed On the
subject.

Heavy being the "hard hitting" part of the equation. Sorry I didn't clarify.

If you measure true momentum a heavy arrow might win, but we as a sporting culture use KE. Ever seen a rifle round's listed as kg/m/s. Would you rather be hit by a 18 wheeler going 2mph or a marble going 1000mph. Physics confused by marketing I think has created one of the best debate topics ever.

I'm not going to be the one that explains this well,but here it goes. Kinetic is for impact in all directions. This is not what you want for a arrow. Momentum is one direction. Foward. That is the way you want your arrow to be going. Kinetic really means nothing in archery. It's just another marketing gimmick.

If you think kinetic is what you have to have in archery go find you a recurve man.

Here's a test for you. Get a good two blade head. Something that can take a hard hit. Get you a 55 gallon still drum. Fill it full of water. Now shoot your riffle through the side of that barrel. Now shoot your arrow through the side. That will show you the difference in kinetic (all direction energy) and momentum( Foward energy)

Ok. What that article neglects to point out is the relation of total arrow weight to FOC and spine. And without that information it is easy to think it can be achieved without sacrificing something.

Like I have said every time, you can get a 16% FOC pretty easy but not with the current arrow you shoot, and no where near the same total arrow weight or speed.

High or above average FOC means you have to build a heavy slow arrow. Average FOC means you can buy just about any properly spined arrow and shoot standard components and normal weight broadheads and shoot higher speeds.

Play around with this to see what you come up with. Adding another 100 grains to the front would get you over 16% but it will under spine your arrows and get them way over your current weight. And that will slow you down.

Go to the build your arrow on this web site and you can play with the numbers and get yourself close. Good luck.

I'm not going to be the one that explains this well,but here it goes. Kinetic is for impact in all directions. This is not what you want for a arrow. Momentum is one direction. Foward. That is the way you want your arrow to be going. Kinetic really means nothing in archery. It's just another marketing gimmick.

If you think kinetic is what you have to have in archery go find you a recurve man.

Here's a test for you. Get a good two blade head. Something that can take a hard hit. Get you a 55 gallon still drum. Fill it full of water. Now shoot your riffle through the side of that barrel. Now shoot your arrow through the side. That will show you the difference in kinetic (all direction energy) and momentum( Foward energy)

Question for you...

Can you change the kinetic energy of your bow by changing the tackle? (I'm with you about momentum / kinetic energy, this is a separate discussion study)

On the light end, my bow pushes a 480 grain arrow to about 290 fps. The KE is about 89. If I go with a heavier setup, I'm pushing about a 580 grain arrow to a little over 260 fps... For about 89 foot pounds. If I go up to about 630 grains, my bow will push it to a little over 250 fps... Still 89 foot pounds.

Yes you are correct with your numbers. A lot of people think when you tell them I'm shooting a 600 gn arrow they think man you got lots of kinetic. But in all reality kinetic very seldom changes more then just a little from where you would have been say at 350 gn arrow. But momentum is what gains.

I shot some arrows a while back. Shot a 318 gn it was 74 ke. 429 gn 78 ke. 554 gn 79 ke 603 gn 80 ke 694 gn 81 ke. So as you can see ke did not change much. But the 318 gn was .457 momentum the 694 gn was. .711. Now that is a gain.

So to your question. No. Not shooting same bow at same poundage.

Once you get your set up. What ever that ke is will be roughly the same unless you can speed up that arrow. That's more poundage

Yes you are correct with your numbers. A lot of people think when you tell them I'm shooting a 600 gn arrow they think man you got lots of kinetic. But in all reality kinetic very seldom changes more then just a little from where you would have been say at 350 gn arrow. But momentum is what gains.

I shot some arrows a while back. Shot a 318 gn it was 74 ke. 429 gn 78 ke. 554 gn 79 ke 603 gn 80 ke 694 gn 81 ke. So as you can see ke did not change much. But the 318 gn was .457 momentum the 694 gn was. .711. Now that is a gain.

So to your question. No. Not shooting same bow at same poundage.

Once you get your set up. What ever that ke is will be roughly the same unless you can speed up that arrow. That's more poundage

KE didn't increase in a linear fashion because velocity is squared in the formula. Logic (and basic physics) dictate that a increase in projectile weight will be accompanied by a proportional decrease in velocity all other things being constant(which they are I assume). You can't compare the two, the math is simply too different. I agree with what you are saying in principal but there is no mystery to the equation, it's basic math.

Yes, leave in tip. Two ways to do AMO FOC calculation: 1. (recommended) measure from knock point to back of field tip; 2. measures from knock point to end of field tip. Both leave in point for balance purposes, then you subtract the difference of midpoint measurement and balance point, Put numbers into calculator and you'll get FOC %. Pushbutton you are on the right path. Dr. Ashby has conducted tests with thousands of shots on actual animals (usually fresh kills) over the course of some 25 years. I believe the Alaska Bowhunter Supply commercial site has his reports as well as a forum called Traditional Bowhunter. By the way, when I increased the weight and FOC of my arrows, I only had to cut about half an inch off to maintain spine stiffness. (However, I'm shooting a 50# recurve, and the arrows were Warrior 400s at 32 inches to start with, and my drawlength is 27-1/2"). Ashby's research also finds heavy and high FOC arrows used by Papua New Guinea tribes(in person field research) and North American Plains Indians (weighed and measured museum arrows).

KE didn't increase in a linear fashion because velocity is squared in the formula. Logic (and basic physics) dictate that a increase in projectile weight will be accompanied by a proportional decrease in velocity all other things being constant(which they are I assume). You can't compare the two, the math is simply too different. I agree with what you are saying in principal but there is no mystery to the equation, it's basic math.

The only thing I don't agree with is that the reduction in velocity isn't necessarily constant. At heavier arrow weights my bow outperforms the calculators and underperforms projections with lighter arrows. The bow is more efficient with more resistance. Even so, with the same broadhead I know that a 580 grain arrow at about 260 fps is going to penetrate better against a tough target than a 480 grain arrow at about 290 fps (which is to say nothing about their relative adequacy or merits), yet the kinetic energy is virtually identical. Using momentum you can get a much better idea about the penetrative potential and make more accurate predictions about real-world performance than you can with KE...

But it's all nitpicky BS to a large extent. We should all just be shooting what we like to shoot, killing stuff and eating it.

The only thing I don't agree with is that the reduction in velocity isn't necessarily constant. At heavier arrow weights my bow outperforms the calculators and underperforms projections with lighter arrows. The bow is more efficient with more resistance. Even so, with the same broadhead I know that a 580 grain arrow at about 260 fps is going to penetrate better against a tough target than a 480 grain arrow at about 290 fps (which is to say nothing about their relative adequacy or merits), yet the kinetic energy is virtually identical. Using momentum you can get a much better idea about the penetrative potential and make more accurate predictions about real-world performance than you can with KE...

But it's all nitpicky BS to a large extent. We should all just be shooting what we like to shoot, killing stuff and eating it.

there are things (like broadhead desgin) which have a much greater impact on terminal performance of an arrow regardless of FOC, momentum and/or KE. these are simply numbers based off calculations. most properly tuned bows are more efficient with a heavier payload, this we know. a great example of this is the manifestation of hand shock or added noise on the release in a bow using a lighter payload. the most important thing to remember here (and i like having these discussion btw) is that these numbers are simply reference points. while they may give us some insight into terminal perfromance they by no means are a be all end all. i will build arrows based on what my customers want first and foremost, all i can do is point them in what i believe to be the right direction. i get some crazy requests, but to each is own.

The only thing I don't agree with is that the reduction in velocity isn't necessarily constant. At heavier arrow weights my bow outperforms the calculators and underperforms projections with lighter arrows. The bow is more efficient with more resistance. Even so, with the same broadhead I know that a 580 grain arrow at about 260 fps is going to penetrate better against a tough target than a 480 grain arrow at about 290 fps (which is to say nothing about their relative adequacy or merits), yet the kinetic energy is virtually identical. Using momentum you can get a much better idea about the penetrative potential and make more accurate predictions about real-world performance than you can with KE...

But it's all nitpicky BS to a large extent. We should all just be shooting what we like to shoot, killing stuff and eating it.

A Shooting Chrony alpha isn't a bad option if, like me, you can't afford an Oehler... More "fliers" and you need a larger sample to get the same data quality, but it generally tracks reasonably well with the top of the line.

My bow starts gaining above 500 gn and really gains at 1080 gn. According to a calculator. My bow will shoot a 1080 at 71.7 fps. It shot it at 187 ft. You have to tell the calculated my ibo is 475 fps for that to work out.

That arrow is for the small white tail. Just want to make sure it makes a pass through.

So I spent some time quizzing one of our guys at work with a PhD in physics. Turns out I should be quieter with some of my opinions. Lol. Not the first time. Momentum wins due to impulse changes and force of impact. So heavy will always out penetrate light out of the same bow. All that is left is balancing the trajectory trade offs.

But what are the trade offs. I've been shooting in the low to mid 500 gn arrows. While doing some testing the other day I was thinking something was wrong with my bow. Loud at the shot. Went and checked the arrow I was testing. It was around 435. Dang what a difference in sound with a 100 gn extra.

You always see where people post that lighter arrows are better in case you miss judge your yardage. But in all reality. Most of us hunt from a stand and feeder at a none yardage. At that point speed does not matter.

there are things (like broadhead desgin) which have a much greater impact on terminal performance of an arrow regardless of FOC, momentum and/or KE. these are simply numbers based off calculations. most properly tuned bows are more efficient with a heavier payload, this we know. a great example of this is the manifestation of hand shock or added noise on the release in a bow using a lighter payload. the most important thing to remember here (and i like having these discussion btw) is that these numbers are simply reference points. while they may give us some insight into terminal perfromance they by no means are a be all end all. i will build arrows based on what my customers want first and foremost, all i can do is point them in what i believe to be the right direction. i get some crazy requests, but to each is own.

If I may I would like to add a bit to this discussion. I believe, when were talking penetration, that if you have an arrow that does not have all the mass behind it, i.e. properly tuned for optimum straight arrow flight, then you loose the power of the arrow mass, speed and wt. If that arrow goes in a bit off center then it does not have the force, be it KE or Momentum, to drive that BH as efficiently as it should. Tuning is just as important as the other factors. I am following and this is very interesting, by now you all know I am not one of the techy's on here. Watching, listening, learning, thinking.

Yes tuning is a major factor in this. So is correct spine. We all can get a weak arrow to shoot bullet holes. Flight is great. But penetration is bad. Then we start blaming the broadheads. But what is happening is that when the arrow makes contact with the animal the weak arrow will flex which now causes the shaft to hit the animal side ways. This is what causes bad penetration. Easy to see. Get a tuff target. Shoot a stiff arrow in to it and watch the shaft. Then shoot a weak arrow and watch. It looks like a antenna after you bent it over and let go.

heavy/efoc arrows have their place in the hunting world, without a doubt but the average hunter stands more to gain from tightening his/her pins gaps (effectively increasing point blank range) while shooting an arrow with a decent amount of grains per # of draw weight. I have found that around 7 grains per # of draw weight we can still build an arrow that:
1. decreases vertical stringing due to a slightly faster trajectory
2. has good foc in the 18%+ range
3. provides good penetration characteristics
4. maintains proper efficiency with the bow
and
5. are forgiving in flight

I don't due extreme hunting so I don't really need an extreme arrow set-up. I feel we can still build arrows that will get us to the target quickly, quietly and efficiently while increasing our overall chances of success.